You may have heard or noticed that meteorologists and climatologists have different start and end dates for the seasons (fall, winter, spring, summer) than the “regular” or astronomical seasons. Although it may seem strange, here is the reason why from the National Oceanic and Atmospheric Administration.
Astronomical seasons are based off of the position of the earth in relation to the sun. The meteorological seasons are based on the annual temperature cycle.
The natural rotation of the earth forms the basis for the astronomical calendar, which defines the seasons with two solstices and two equinoxes. Earth’s tilt and the sun’s alignment over the equator determine both solstices and equinoxes.
The equinoxes mark the times when the sun passes directly above the equator. In the Northern Hemisphere, the winter solstice is on or around December 22. This year it is on Thursday, December 21st at 11:28 AM ET.
But, because Earth actually travels around the sun in 365.24 days, an extra day is needed every fourth year, creating what we know as Leap Year. This also causes the exact date of the solstices and equinoxes to vary.
For that reason, the variation of the season start dates and lengths makes it hard for meteorologists and climatologists to consistently compare seasons. For that reason, the meteorological seasons were born.
Meteorologists and climatologists break down the seasons into groupings of three months based on the annual temperature cycle as well as our calendar. We generally think of winter as the coldest time of the year, so the months of December, January, and February fall in the winter category.
With the meteorological seasons, it becomes much easier to calculate seasonal statistics from the monthly statistics, both of which are very useful for agriculture, commerce, and a variety of other purposes.
Average high and low temperatures follow in Saginaw and Flint:
December: High: 33.5 Low: 21.2
January: High: 28.9 Low:15.6
February: High:31.7 Low: 17.3
December: High: 34.1 Low: 20.8
January: High: 29.6 Low:15.3
February: High: 32.8 Low: 16.9
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